Iowa ? Federal immigration agents raided a northeastern Iowa meat processing plant Monday, arresting more than 300 people and housing many of them at a converted fairgrounds.

The raid of the Agriprocessors Inc. plant in Postville was the largest in state history and had been planned for months, said U.S. Attorney Matt M. Dummermuth.

The raid, one of several conducted at meat-processing plants around the country in recent years, was aimed at seeking evidence of identity theft, stolen Social Security numbers and people who are in the country illegally, Immigration and Customs Enforcement spokesman Tim Counts said.

Agriprocessors, the world’s largest kosher meatpacking plant, did not return messages seeking comment.

Of those arrested, 44 were released for humanitarian reasons, primarily because they must care for children. They were ordered to report to court later.

Others arrested were held in local jails or driven by bus about 75 miles to temporary housing at the National Cattle Congress fairgrounds in Waterloo. Federal authorities previously leased the fairgrounds and have turned it into a secure center.